Motor-control system



L. J. STEPHENSON.

MOTOR CONTROL SYSTEM.

APPLICATION FILED NOV.28, 1919.

Patented Apr. 4, 1922.

LEIGH a". srnrnnnson, or CHICAGO, ILLINoIs, ASSIGN OR TOTWILLIAMT; FENTON,

BENJAMIN BECKER, LYNN A. WILLIAMS, GEORGE B. BURRA STEPHENSON, TRUSTEES, ALL OF CHICAGOQILLINOIS.

G ,AND LEIGH J.

Moron-common srsrn'm,

Specification of Letters Patent. 'Pdtented Apr, 4, 1922,

Application filed November 28,1919; Serial No. 341,247.

To all whom it wutg concern:

it known that I, LEIGH .lnS'rnrrnsNsoX, a citizen of the United States, residing at hicago, in the county oi Cook and State oi? Illinois, have invented aficertain new and useful lnfiprovement in Motor-Control Systems, ct which the following is a full, clear, concise, and-exact description, retereme being had to the accompanying drawings iormiinga part of this specification.

My invention relates to improvements in motor control and is especially concerned with the provision of novel means for controlling the operation oi motors designed for operating mill rolls,hoists, etc, wherein the motors are driven directly from a-source of direct current, a dynamobeing connected in series with the motor and controlled in such a manner that during the initial portion of the accelerating period of the motor the dynamo opposes the potential of the source of current supplying current to the motoiu and during the subsequent period of ac cele'ration adds its voltage to that oi the sourceol supply so as to increase the potential applied to the motor terminals any desired amount above the potential of the source of supply.

The objects of my invention are: Firsti ter described whereby the motor can be rapidly and smoothlyaccelerated and held at anydesired speed;

Second: To provide means for controlling a motor wherebyit can be caused to function exactly like a series motor or if desired. can be caused to accelerate like a series motor but which will have a constant top speed;

Third: To provide a motor control ofsinr ple construction by means of which the speed of the motor can be quickly reduced through regenerative braking;

' Fourth; To provide means for controlling the operation of the motor which will require minimum number of switches and which is otherwise simple in construction, economical to manufacture and easy to operate,

Other objects will appear as this description progresses, reference being had. to the aceompanying drawings in whici Y Figurel is a diagrammatical sketch of the apparatus electrical connections com: prising my improved motor control; and \i To provide means of the charac- Figure 2 is a similar view of a modified form ofmy invention. a I I In my Patent, Number 1,322,4T1bt November 18, 1919, I have described a dynamo electric machine comprising amotor having a lield winding, regulating dynamo connected in series with the motor field Winding to form afield winding circuit, and means for lmpressing a potential upon Said field winding circuit in a direction to oppose the counter-electromotive force of the regulating dynamo. 'The regulating dynamo is me: clianically connected with the motor so as to rotate at a speed constantly proportional to the speed otthe motor. The field winding of the regulating dynamo is connected with the field winding of the motor in such a manner as to maintain a constant ratio between the currents flowing in these two field windings. A rheostat is connected with the fieldwinding of the regulating dynamo by means of which the ratio of the currents flowing in the field winding of the'motor and the field winding of the regulating dynamo can beivaried as desired to control the operation of the motor.

One of the objects of my present invention is to take advantage oi: the peculiar istics, and by means of which regenerative braking can be easily and efiiciently effected. Referring to the drawings, the reference character M indicates the motor designed to be used for driving the various kinds of characteristics of the dynamo electricmaapparatus, above referred to, which is supplied with current from the direct current mains 5 and 6. Connected in series with they motor M is'a dynamo D driven at a constant Speed, by a mot'orM connected directly across the lines 5 and 6. The motor M 15 so ("lesigned that its normal voltage is twice "that of the lines 5 and 6, and the dynamo D is so designed that its maximum voltageis equal to the voltage of the lines 5 and 6. .l 'provide means, which I shall shortly describe in detail, for causing the dynamo D initially generate a voltage equal to line voltage, but in a direction opposing line voltage so that the resultant voltage impressed upon the terminals 01" the motor M will be zero. I also provide means for sub sequent-1y gradually but rapidly decreasing the voltage of the dynamo D until it reaches a zero value, and for then reversing the direction of the voltage of the dynamo D and gradually but rapidly increasing its voltage in the reversed direction until its generated voltage is substantially ecual to that of the line and added to that of the line. By means of this apparatus I am enabled to gradually but rapidly increase the voltage applied to the terminals of the motor from zero to sub stantially twice line voltage, thereby causing it to rapidly accelerate. I also provide means for initially fully exciting the fields of the motor so as to provide a strong starting torque, and means for subsequently causing a rapid decrease in the field strength of the motor whereby due to this additional cause, its speed will rapidly increase, this means being controlled by the voltage impressed upon the motor armature terminals.

I shall now describe in detail the means by which I cause the voltage of the dynamo D to decrease from the maximum value to zero then reverse and build up in the opposite direction to its maximum. The dynamo D is provided with a field winding 7 which is connected in series with the armature 8 of the generator G to form a field winding circuit which is connected directly across the lines 5-6, as shown. The generator G is driven by a motor M the armature 9 of which is connected directly across the lines 5-45. The field winding 10 of the motor M is connected in series with the armature 11 oi the regulating dynamo RD to form a field winding circuit which is likewise con nected across the lines 5-6. The regulating dynamo ED is provided with a field winding 12 which is connected in parallel with the field winding 10 of the motor M the current through the field winding 12 being controlled by an adjustable rheostat 13. The field winding 14 of the generator G is connected around or in parallel with the armature ll. of the regulating dynamo RD. An adjustable rheostat 15 is connected in series with the field winding 14 of the generator merely for the purpose of adjusting the voltage of the generator G, and is not used for control purposes, that is, after once being set to produce a desired operation, it is thereafter undisturbed.

When the adjustable rheostat 13 is adjusted so as to open the field circuit of the regulating dynamo RD the generated volt age of the regulating dynamo will be substantially zero and consequently no current will flow through the field winding 14L of the generator (5: and its voltage will be substantially ZQIO. There is, therefore, nothing to oppose the flow of current through the field winding 7 ol the dynamo D and its field winding will be fully excited. Since the dynamo D is operating at a constant speed. it will be generating its highest poten tial. This potential opposes the line voltand consequently reduces the potential ZillllllPfl to the terminals of the motor M to substantially zero. At this time the field the motor M will be fully excited through the following circuit: line wire 5, conductor 16. versmg switch 17, field winding 18,

conductor 19, armature 20 of regulating dynamo 111),, to line wire 6. If the adjustable resistance 13 is now actuated to cut out all 01" its resistance so as to permit a maximum How of current through the field wind- 11 12 ot the regulating dynamo RI), two things are accomplished. In the first place, the counter-clectromotive force of the regulating dynamo will rapidly increase and since this couuter-electromotive force opposes the flow oi? current through the motor field winding 10, the motor M will be caused to correspon:lingly rapidly accelerate, there by causing the armature of the generator G lo accelerate rapidly. In the second place the generated voltage of the regulating dynamo RD will, as stated, rapidly increase and cause a corresponding rapid increase in the flow oi? current through the field winding 1% of the generator G. The rapid acceleration of the speed of the armature ot' the ;cncrator ('land the rapid increase in its neld strength will cause a corresponding rapid increase of its voltage, and since this voltage opposes the voltage impressed on the field winding 7 of the dynamo D, the current flowing through this field winding will be rapidly decreased and effect a corrcsponding reduction in the potential of the dynamo D. Inasmuch as the dynamo D opposes the line voltage, any decrease in the potential of the dynamo D will cause a corresponding increase in the potential applied. to the terminals ot the motor M, and thereby cause it to accelerate.

As the speed of the motor M increases, a point will be reached where the potential of the generator G will equal that of the line, and as a result no current will flow through the field winding 7 and the potential of the dynamo D will be substantially zero. At this point full line voltage is being impressed upon the terminals of the motor M.

As the motor M continues to increase in speed, the voltage of the generator G will rise above line voltage and cause current to flow through the field winding 7 of the dy,

namo D in a direction opposite to that in which the current initially fiowed through this winding, thereby reversing the direction of the potential of the dynamo D so that its potential is now added to the line potential, thereby causing a still further increase in the speed of themo'tor M. The

motor hi continues to increase in speed until the generator G is generating substantially twice line voltage, thereby causing the dynamo D to generate substantially full line voltage. Since the voltage of dynamo D is added to line voltage, this means that substantially double line voltage is being impressed upon the terminals of the motor M. Having'thus described the means which I employ for controlling the potential applied to the terminals ofthe motor M, I shall now describe the means by which I control the field strength of the motor M.

The motor M is provided with a field winding 18which is connected in series with the armature 20 of the regulating dynamo RD through a reversing switch 17 to ,form a field winding circuit for the motor M, which is connected directly across the-lines 5-43. The counter-electromotive force of the regulating dynamo RD is opposed to the potential impressed on the field winding circuit by the lines 56, so that as its counter-electromotive force increases, the ciu'rent flowing through the field winding 18 will be correspondingly decreased.

The regulating dynamo RD, has a field winding 23 which is connected in parallel with the field winding 18 of the motor M, so as to maintain a constant ratio between the currents flowing inthe motor field Wind ing 18 and the regulating dynamo field winding This ratio can be varied by means of the adjustable rheostat 24 which is connected in series with the field winding 23. The circuit of the field winding 23 includes a solenoid-operated switch 27 the solenoid 28 of which isconnected directly across the terminals of the motor M]. The circuit of the field winding 23 also contains a reversing switch 29.

The, switch 27 is designed that it will close when the potential across the terminals i of the motor M has reached any predetermined desired value, whereupon current will flow through field winding 23 of the regulating dynamo RD causing its potential to rapidly increase and since the counter-electromotive-force of this regulating dynamo opposes the potential impressed upon the field winding 18 of the motor, there will be a corresponding rapid decrease in the field strength of the motor M, causing it to accelerate. This causes the regulating dynamo RD to accelerate at the same rate and increase its voltage, thereby causing a substantial decrease in the field strength of the motor M and a further increase in the speed of the motor. This cycle continues until the motor reaches its top speed, which is'determined by the relative designs of the motor M and the regulating dynamo RD, as explained in mypatent referred to above;

When it is desired to stop the motor,- the adjustable resistances 13 and 24 are actuated to gradually include their resistances in the circuits in which they are connected. After the resistance of therheostat 13 is included in the circuit of-the field winding 12, the

field strength and consequently the voltage of the regulating dynamo RD will decrease, thereby causing an increase in the current flowing in the field winding 10 of the motor M and'a decrease of the current flowing in the field winding 14: of the generator G. By increasingthe field strengthoi the motor M its speed is reduced, as is also the speed of the generator G, andthe regulating dynamo RD. Due to the combined weakening of the field oi the generator G and thereduction in the speed of its armature, its voltage will rapidly decrease thereby causing rapid de-' crease inthe field strength'oit the dynamo D and a corresponding reduction in itspotential. r

At the same timethat the effects resulting from the weakening of the field oi: the regulating dynamo take place, the field strength of the dynamo RD is being decreased by reasonof the inclusion of resistance 24- in its field winding circuit. This decreasein the field strength'ofthe regulating dynamo RD results in an increase in the field strength of the motor M and a correspondingincrease in its potential. thereby raising its potential above the combined potentials of the line and the dynamoD, causing the dynamo D to function as a motor to drive the motor M as a generator to return current to the line. i

'As the resistances 13'and 2-4 are continuously cut into their respective circuits,-the actions justdescribed continue until the potential applied to the solenoid 28 of the switch 27 decreases to'such an extent that this switch opens, thereby reducing the field and consequently the [counter-electromotive force of the regulating dynamo RD to zero and bringing the field strength of the motor M toamaximum. The-point is also reached where the voltage of thegenerator G just equals the line voltage and the field of the dynamo D is reduced/to Zero. The field is then reversed by a continued decrease in the'voltage of the generator G, so that its generated voltage now 'beings'to oppose'line voltage. The reduction in the potential applied to' the motor terminals'due to the opposing action of the dynamo Dand the increase in the generated voltage of'the motor M,'due" to its increase in field strength," will: tend to maintain the voltage of the motorM at a value greater than the algebraic sum of the dynamo voltage and the line voltage, thereby causing the motor M to continue to act as'a generator and return current to the line until the motor is brought to, practically a standstill; T

Because durlng regeneration the algebraic sum of the line voltage and the potential ol the dynamo l) is constantly diminishing at substantially the same rate that the motor generated voltage decreases, the current returned to the line by the motor will remain substantially constant.

To reverse the direction of rotation of the Motor M, it is merely necessary to operate the reversing switches 17 and 29, respectively.

The construction illustrated in Figure 2 is substantially-the same as that shown in Figure 1, except that the generator G is dispensed with and the dynamo is provided with a double field winding so arranged and connected that during the first portion of the acceleration period the current will flow through one half of the field winding to cause the voltage of the dynamo D to oppose line voltage, and during the remaining portion of the acceleration, current will flow through the other half ot the dynamo field winding in such a direction as to cause the dynamo D to generate a voltage in phase with line voltage.

In this construction the motor M, is connected with the regulating dynamo RD in the same manner as in Figure 1 and the regulating dynamo RD controls the speed of the motor M in the same manner as in Figure 1. The dynamo D, as described above, has two opposed field windings 7 and 7. respectively. The two field windings 7 and 7 are connected in series and directly across to the line. The armature oi the regulating dynamo RD is connected in parallel with the field winding 7.

With current applied to the line wires and 6 and the adjustable rheostats -3 and 24 adjusted to open the respective circuits in which they are connected, thevoltage of the regulating dynamo RD will be substair tially zero and consequently current will flow from the line through the conductors 40, ll and 42, through the regulating dynamo RD, conductor 43, field winding 7 and conductor 44 to line 6, the current choosing the path through the regulating dynamo RD, in preference to the field winding 7, because of the low resistance of the former path and comparatively high resistance of the latter. When, however, the rheostat 13 is actuated to closethe field winding circuit of the regulating dynamo RD and the resistance 13 is cut out, the motor M and the regulating dynamo RD will rapidly accelerate for the reasons stated in connection with Figure 1, and cause a corresponding rapid increase in the counter-electromotive force of the regulating dynamo RD. This increase in the counterelectromotive force of the regulating dynamo RD will offer a rapidly increasing opposition to the passage of current through it to the field winding 7, and cause a corresponding increase in the flow of current through the field winding 7 until when the regulating dynamo RD is generating half line voltage the currents flowing in the field windings T and 7 will be equal, and the voltage of the dynamo D will be reduced to zero. As the speed and counter-electromotive force of the regulating dynamo RD continue to increase, the current in the field winding 7 will be still further diminished and the current in the field winding 7 increased until. the counter-cl*ctromotive torce ot the regulating dynamo RD reaches its maximum value. at which time there will be substantially no current flowing in the field wii'iding T and full current flowing in the field winding 7, thereby causing the dynamo D to add its full potential to the line voltage, as a result of which double the line voltage is applied to the terminals oi the motor M just the same as in Figure 1.

it is believed unnecessary to describe the remaining features of the construction illustrated in F igure 2 for the reason that they are the same as those illustrated in l igure l, and operate in exactly the same manner. In stopping the motor, the rheostats 13 and 241; are actuated as in Figure l to gradually include the resistances 13 and 2% in the respective circuits, whereby the counter-electromotive force of the regulating dynamo (\D is gradually decreased and the field strength of the motor M gradually increased, so as to cause a reduction in the generated voltage of the dynamo D. Likewise the counterelectromotive force of the regulating dynamo RD is reduced when the circuit through the relay 27 is opened, causing a strengthening of the field 18 of the motor M, with the consequent return of power to the line, as described in connection with Figure 1.

lVhile I have described the details of the lzlGiliCllGd embodiments of my invention, it is to be clearly understood that my invention is not limited to these details, but is capable of other adaptations and modifications within the scope of the appended claims.

Having described my invention, what I claim as new is:

1. The combination with a power motor of a dynamo connected in series with said power motor, a second motor to]: driving said dynamo at a siiibstantially constant speed, a field winding for said dynamo. a generator connected in series with said field winding to form a field winding circuit, means for impressing a potential upon said field winding circuit in a direction to oppose i the voltage of said generator, a third motor for drivin said 'encrator a field windin 17 b 3 O for said third motor, a regulating dynamo connected 1n series with sald third motor field winding to form a field WlIlCllIlg C11- cuit, means for impressing a potential upon said last-named field winding circuit in a direction to oppose the counter-electromotive force of said regulating dynamo, driving connections between said motor and said generator and regulating dynamo whereby said generator and regulating dynamo operate at speeds constantly proportional to the speed of said third motor, afield winding for said generator connected across the armature of said regulating dynanm, a ield winding for said regulating dynamo connected with said third motor field winding so as to maintain a constant ratio between the rurrents flowing in said two last mentioned field windings,means for varying said ratio, a field winding for said power motor, a second regulating dynamo connected in series with said power motor'field winding to form a thirdfield winding circuit, m ans for impressing a potential upon said third field winding circuit in a direction to oppose lthe' counter-olectromotive force at said second regulating dynamo, a field winding circuit for said second regulating dynamo connected with the field winding of said power motor in such a mannor as to maintain a constant ratio between the currents flowing in said last mentioned field winding circuit and said power motor field windi the said last mentioned field winding circuit com 'rlsing a switch, an adjustable rhoostat for lent-rolling the fiow oi current in said second regulating dynamo field circuit, ineans for causing saidsecond regulating dynamo to rotate at a speed constantly proportional to the speed of said power motor, and means controlled by the voltage applied to said power motor terminals for controlling the operation of said switch.

2. The combination with a power motor or" means for supplying current to said motor, a dynamo connected in series with said motor, a field winding for said dynamo, a generator connected in series with said field winding to form a field winding circuit, means for impressing a potential on said field winding circuit in a direction opposite to the voltage of said generator, the maximum voltage of said generator being greater than said impressed potential, means 'l or'causing the voltage of said generator to rapidly increase to its maximum value comprising a field winding for said generator, a regulating dynamo the field wvmdmg of said generator being connected across said regulating dynamo, and means l'or causing the voltage of said regulating dynamo to rapidly increase, and other means for causing said power motor to rapidly accelerate comprising a field winding for said power motor, a regulating dynamo connected in series with said power motor field winding to form a power motor field winding circuit, means for impressing a potential on said power motor field winding circuit in a direction to oppose the counter-electrogenerator connected in series with said field winding to form a field winding means for impressing potential on said field winding): circuit in a direction opposite tothe voltage of said generator, the maxiinum volt e oi? said generator being greater than said impressed potential, means 101' causing the voltage of said generator to circuit,

rapidly increase to its maximum value com-.

prisi a field winding for said generator, a c1 m I X regulating dynamo, the field windin or said generatorheing connected across said regulatingdynamo, and means for causing the voltage oi said regulating dynamoto rapic y increase and other means for causing sa d power motor to rapidly accelerate after the voltage of said generator hasincreased to a value greater than the potential impressed on dynamo field winding circuit The con'ihination with a power motor oil means for su fnplying current to'sa-id ino-- tor, a dynamo connected in series with said motor, a field winding For said dynamo, a gene ator connected in series with said field winding to form a field winding circuit, means 'lor impressing a potential on said field winding circuit in a direction opposite to the voltage of said generator, the maximum voltage of said gei'ierator being greater than said impressed potential, means for causing the voltage of said generator to rapidly increase to its maximum value, and other means for causing said power motor to rapidly accelerate after the voltage of said generator has increased to a value greater than the potential impressed on said dynamo field winding circuit.

5. The combination with a power motor of means for supplying current to said motor, dynamo connected in series with said motor, a field winding for said dynamo, a generator connected in series with said field winding to form a field winding circuit, means for impressing a potential on said field winding circuit in a direction opposite to the voltage said generator, the maximum voltage of said generator being greater than said impressed potential, means for causing the voltage oi said generator to rapidly increase to its maximum value, and

other means for causingsaid power motor to rapidly accelerate comprising a field winding for said power motor a regulating dynamo connected in series with said power motor field wii'iding to form a power motor field winding circuit, means tor impressing apotential on said power motor field winding circuit in a direction to oppose the counterelectromotive force. oi said regulating dynamo, a switch in said power motor field winding circuit, and means for causing said switch to be controlled by the voltage inipressed on said power motor terminals.

6. The combination with a motor of a source for supplying current to said motor, a dynamo connected in series with said motor, a field winding for said dynamo, means for causing current to initially flow through said field winding in one direction and subsequently in the other direction whereby said dynamo first opposes the potential impressed on said motor terminals and subsequently adds its potential to the potential of said source, a field winding For said motor, means tor supplying current to said field winding, means "for reducing the flow of current in said field winding, and means for causing said last-nametl means to become 0perative only after the flow of current through said dynamo field winding has lQ-YQISGCl.

7. The combination with a motor having a field winding, of means for supplying current to said motor, a dynamo connected in series with said motor, means for reversing the direction of the generated voltage of said dynamo, means for supplying current to the field winding of said motor, and means controlled by the potential applied to said motor terminals for reducing the supply oi current to said motor field Winding.

8. The combination with a motor of means for impressing a gradually increasing voltage upon the terminals thereof, and means controlled by the potential impressed on said motor terminals for decreasing the field strength of said motor after the potential applied to its terminals has reached a predetermined value.

9. The combination. with a motor of means for impressing a gradually increasing voltage upon the terminals thcreot, and means controlled by the potential impressed on said motor terminals for decreasing the field strength of said motor,

10. The combination with a dynamo having a field winding, of a generator connected in series with said winding to form a field winding circuit, means for impressing a potential on said field winding circuit in a direction to oppose the voltage of said generator, the maximum voltage of said generator being greater than the potential inipressed on said field winding circuit, and means for rapidly accelerating said generator, comprising a motor having a field winding, a regulating dynamo connected in series with said field wini'ling to form a field winding circuit, and means For impressing a potential on said field winding circuit in a direction to oppose the counter-electromotive force of said regulating dynamo.

In 'itness whereof, I hereunto subscribe my name this 26th day of November, 1919.

LEIGH J. STEPHENSON. lVitnesses ANDREW lVmTnncoRN, EDNA V. GUs'rAFsoN. 

